Since the first printing press was placed into operation, operators have wrestled with the problem of freshly printed sheets becoming undesirably marked as they travel from one printing station to the next. To solve this problem, press manufacturers and innovators have tried various methods ranging from tracking/skeleton wheels, pneumatic devices, to cylindrical coverings of sandpaper, glass beaded paper, dimpled metal and loose mesh fabric. While most of these devices are effective to some degree, none of them fully satisfy the needs of a printer. A brief history illustrating the development of such anti-marking systems is outlined below.
In U.S. Pat. No. 2,085,845, Binkley applies “a coating granular material such as silicon carbide, emery, etc.” onto the face of the fabric which has a barrier coating adhered onto rear side and is adhered to the make-ready and then clamped to the tympan roll. Here, Binkley asserts that using a sandpaper-like material will provide the advantage of decreasing the marking of freshly printed sheets. In U.S. Pat. No. 2,555,319, Cross also studies the application of granular materials to rolls within a printing machine and tests granular materials ranging from glass culets, silicon carbide and aluminum oxide and compares them to spherical glass beads. He asserts that the spherical glass beads offer a smooth and round uniform surface that is superior to that of granular grit. Cross further asserts that spherical beads allow the freshly printed/inked sheet to be uniformly supported by the tops of millions of uniform glass beads resulting in a decrease of marking printed sheets. Cross also teaches of both the benefits of back coating a porous substrate and over-coating the beaded side to improve adhesion of the glass beads to the substrate as well as to aid in repelling printing inks/solvents.
In U.S. Pat. No. 4,694,750, Greene attempts to improve on known rolls having granular surfaces by using “an elastic member that is attachable to each flange and is stretchably positionable around the circumferential granular surface.” Greene's use of elastic bands to make an easily installable anti-marking product falls short in two areas: first the elastic bands impede use of the full width of the cylinder (thus limit sheet size). Second, since the elastic bands run circumferentially around the cylinder, they do not provide adequate uniform tension across the entire sheet resulting in movement of the granular sheet and ultimately marking results.
In U.S. Pat. No. 4,688,784, Wirz employs perforations in various textured surfaced anti-marking sheets that come into alignment with a hole or bore of the air ducts in the cylinder. The purpose of using compressed air is to aide in the transport of the freshly printed sheet as it travels mark-free from one printing station to the next.
In U.S. Pat. No. 3,791,641, DeMoore uses an ink repellent PTFE sheet that is affixed to skeleton wheel. Later, in U.S. Pat. No. 4,402,267, DeMoore improves upon this design by adding “a loosely retained ink repellent fabric covering” known in the industry as SUPER BLUE™ over the cylinder sheet. In U.S. Pat. No. 5,842,412, Greenway et al. also uses a light weight fabric with preferred axial air permeability not less than about 0.138 cfm and a surface structure with closely spaced features of a spacing not more than about 0.125 inch.” This fabric is known in the industry as QUACK™.
In U.S. Pat. No. 6,203,914 B1, Sudo et al. follows Cross's process for manufacturing an ink repellent anti-marking sheet as disclosed in U.S. Pat. No. 2,555,319. Sudo uses a urethane crosslinked silicone top coat well known in the industry and disclosed in U.S. Pat. No. 5,415,935 as an ink-repellent coating over the glass beaded surface.
In U.S. Pat. No. 6,244,178 B1, DeMoore recognizes the importance of easy installibility and further improves his SUPER BLUE™ fabric to include asserted improvements such as pre-stretched, pressed flat and pre-cut to the cylinder dimensions complete with anti static/conductive filaments and ink-repellent coating.
Despite the efforts made in these many patents or products in the market today, marking of printed sheets in printing presses remains problematic.